The present invention relates generally to fluid property measurement in a subterranean well and, in an embodiment described herein, more particularly provides fluid property sensors and methods of calibrating same.
It is very beneficial to be able to independently control production from each one of multiple zones of a well. For example, when water begins to be produced from a particular zone, it may be desired to cease production from that zone, while still producing from other zones of the well. As another example, when gas begins to be produced from a particular zone, it may be desired to decrease production from that zone, while still producing from other zones of the well. As a further example, rates of production from various zones may be independently regulated to maximize overall production from a reservoir.
However, in order to accurately determine the particular zones to regulate production from, and the manner in which production from those zones should be regulated, a well operator needs to be able to determine what fluids, and what quantities of those fluids, are being produced from each zone. Prior methods of making these determinations have relied on use of wireline conveyed tools. However, use of these tools usually requires that the well be shut in and that an intervention be made into the well.
It would be far more convenient and useful to be able to continuously monitor what fluids, and what quantities of those fluids, are being produced from each zone of a well. It is accordingly one of the objects of the present invention to provide fluid property sensors for relatively permanent installation in a well, and methods of using and calibrating those sensors.
In carrying out the principles of the present invention, in accordance with embodiments thereof, fluid property sensors and associated methods are described herein. In the described embodiments, the sensors and methods are utilized to facilitate monitoring and control of production from multiple zones of a well. However, it is to be understood that the sensors and methods may also be used in other situations.
In one aspect of the present invention, sensors in fluid communication with an annulus external to a tubing string are used to measure properties of fluid flowing from a zone into the tubing string. By using such external sensors for each zone of a well, properties of the fluid produced from each zone may be determined prior to the fluid entering the tubing string. Thus, the properties measured by the external sensors are indicative of the fluid produced from a zone prior to it being commingled in the tubing string with fluid produced from other zones.
In another aspect of the present invention, an external venturi flowmeter is provided. The flowmeter is interconnected in a tubing string and positioned in a wellbore. Fluid flowing from a zone through an annulus between the wellbore and the tubing string is constrained to pass through a flow restriction due to a projection formed on a housing of the flowmeter. A differential pressure gauge measures a differential pressure between the fluid upstream of the flow restriction and the fluid flowing in the flow restriction. In this manner, a rate of flow of fluid produced from a zone may be determined before the fluid is commingled in the tubing string with fluid produced from other zones.
In yet another aspect of the present invention, a fluid density sensor is provided. The fluid density sensor uses a unique combination of gamma ray sources and detectors to enable its relatively permanent installation in a well. In the described embodiment, gamma ray sources exempt from certain regulations and Geiger-Muller gamma ray detectors are used. An additional detector is used to determine the contribution of background gamma ray sources to the measured rate of gamma rays received.
In a further aspect of the invention, the fluid density sensor is combined with other sensors in a sensor system, measurements from which may be used to determine a volumetric flow rate of each phase of fluids produced through a tubular string. The sensor system may be positioned in the string downstream of a flow control device regulating fluid flow into the string from a zone.
In a still further aspect of the invention, multiple ones of the sensor systems and flow control devices may be used in a well having multiple independently produced zones. A method of calibrating the sensor systems is provided, whereby measurements obtained from each of the sensor systems may be calibrated. The use of the calibrated multiple sensor systems enables determination of the volumetric flow rate of each phase of fluids produced from each of the zones.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.